Limit switch operating mechanism



y 1954 R. E. MORRIS ETAL 2,679,559

LIMIT SWITCH OPERATING MECHANISM Filed March 26, 1952 2 Sheets-Sheet l INVENTORS LYMA/V .5. LEE

By ROBE RTE. MORRIS ATTORNEY May 25, 1954 R. E. MORRIS ETAL 2,679,559 LIMIT SWITCH OPERATING MECHANISM Filed March 26, 1952 2 Sheets-Sheet .2

INVENTORS 1 LYMA/V 5. LEE

BY ROBE/77' E. MORRIS Patented May 25, 1954 Delaware 2 Claims. 1

This invention relates in general to switch operating mechanism and more particularly to improvements in the type employed in association with actuators for aircraft control devices and components for automatically stopping the actuator motor after a predetermined movement of the actuator in either direction and for preventing motor operation of the actuator screw in either direction and for preventing motor operation of the actuator screw in a given direction after a predetermined extent of movement of the screw in that direction.

One of the primary objects of the invention is to provide a limit switch operating mechanism that will insure the tripping of the limit switches upon the completion of a predetermined linear movement of the actuator screw in .either direction in response to motor operation, through a .gear train, so that if the operator closes the master switch, the motor is ineffective to continue a drive of the actuator screw in that direction and effcctiveto drive it in a reverse direction.

In addition to this object, it has beenobserved that the aircraft ground crew, in assembling the actuator mechanism on the aircraft, are very likely to inadvertently manually rotate the actuator screw relatively to the motor driven torque operating nut. Inasmuch as the limit switches have been spaced for a predetermined length of placement of the screw with respect to the limit switches destroys the very purpose of the limit switches.

It is therefore a primary object of this invention to provide a limit switch operating mechanism that will automatically compensate for such actuator screw adjustment so that it will trip the limit switches at a predetermined screw position regardless of Whether the screw is extended by manually rotating the clevis end of the screw or by the motor through the gear train.

Another object is to provide in a limit switch operating mechanism a limit switch actuating member that is designed to advance at a slower rate of speed than the actuator screw so as to permit location of the limit switches within a relatively small space.

With the foregoing and other objects in view, the invention resides in the combination of parts nd in the details of construction hereinafter set I orth in the following specification, and appended laims certain embodiments thereof being illusrated in the accompanying drawings in which:

Figure 1 is a view, partly in side elevation and artly in longitudinal section showing an elec travel of the actuator screw, this manual dis- UNITED STATES PATENT OFFICE LIMIT SWITCH OPERATING MECHANISM Robert E. Morris, Lyndhurst, and Lyman S. Lee, Shaker Heights, Ohio, assignors to Jack vIt Heintz, Inc., Cleveland, Ohio, a corporation of Application March 26, 1952, Serial No. 278,672

.2 tric motor, an actuating screw driven thereby, a pair of limit switches and the limit switch actuating mechanism.

Figure 2 is a view in cross section taken along line 2-2 of Figure 1; and

Figure 3 is an electrical circuit diagram of the motor and limit switches.

Referringmore particularly to the drawing, the usual reversible electric motor .and gear train driven thereby are enclosed in a housing I with an elbow 2 for suitable electric cables leading to a pair of limit micro switches .3 and 4 of the plunger type having plunger-s 5 and 6 and spaced a predetermined distance apart longitudinally. The micro switches are normally closed and are opened upon depressing .the plungers.

The actuatorscrew, itself, is shown at I, with its outer end carrying a clevis 8 for attachment to the aircraft part to be actuated in either of two reverse directions. Insofar as the elements of the present invention are concerned, suffice it to say that surrounding the actuator screw I is a torque tube 9, supported by bearings It in the housing with clearance around the screw I, and rotatively driven by a suitable gear train driven by the usual reversible electric motor. The torque tube 9 rigidly carries a torque tube nut 9' near its outer end. The .torque tu be nut 9' is provided with internal threads .of comparatively large pitch to mate with corresponding external screw threads on the actuator screw I. The arrangement is such that rotation of the actuator nut 9 causes linear movement of the actuator screw I in a directiondetermined by the direction of rotation of the torque tube nut 9'.

Torque tube 9 is also provided with external screw threads to mate with internal screw threads of a limit switch operating tube II that surrounds torque tube 9. The pitch of the mating threads of torque tube 9 and tube II is approximately one third of that of the mating threads of the actuator screw I and the torque tube nut 9'. At its inner end, the limit switch operating tube ll carries a radially outwardly extending switch tripping member I2. Switch bracket I3, of limit switch 3, carries a leaf spring M with an inwardly extending bent end I 5 to be engaged by switch tripping member I2 and limit switch 4 is similarly provided with a leaf spring [6 carried by bracket I! and provided with a leaf spring I6 carried by bracket I1 and provided with a bent end l8 to be engaged by switch tripping member l2.

The device also includes a dust tube I9 surrounding the switch actuating tube II inside of housing member 20 and secured rigidly at 2| to the actuator screw 1. Moreover, the dust tube I9 is longitudinally splined to the switch actuating screw ll.

Thus, in operation, the torque tube nut 9 revolves about the screw 1 to cause the latter to be extended or retracted in accordance with the direction of rotation of the motor and its gear train. The dust tube, being internally splined along its longitudinal axis, moves linearly with the screw. As the torque tube nut 9' rotates, it also drives the switch actuator tube linearly in direct ratio of, for instance, approximately 3 to 1 ratio to the linear travel of the screw.

The switch tripping member [2 is shown in Figures 1 and 3 in engagement with spring l3 to open limit switch 4. This prevents further retraction of the screw even if the operator should close the master switch for actuator screw operation, which would result only in a reverse operation of the motor, the gear train and the screw for extension of the latter to the left, as viewed in the drawing. This causes the switch actuator tube to move to the left until switch tripping member 12 engages spring IE to open limit switch 3 to make it impossible to extend the screw any further into extended position.

Normally, the actuator screw does not rotate. However, if in installation or manual adjustment,

the actuator screw is rotated manually while the torque tube and its nut are stationary, the dust tube, being splined to the switch actuating tube, causes the latter to revolve on the torque tube, thereby compensating for any adjustment of or external rotation of the screw.

Figure 3 is an electrical circuit diagram showing the motor at 22 and field coils 23 and24 leading respectively to limit micro switches 4 and 9 and and the main manually operated switch 25. Micro switch 3 is for actuator screw retraction. Both of these switches are normally closed. However, when either is tripped by the switch tripping member [2 of the switch actuating tube, that micro limit switch is opened while the other micro switch remains closed. Thus, if the operator closes the main switch 25, while, as shown in Figures l and 3, limit micro switch 4 is open and switch 3 is closed, the motor cannot rotate in a direction to further retract the fully retracted actuator screw but is energized to rotate in a direction to extend the actuator screw until micro limit switch 3 is tripped to open position.

It will therefore be seen that there has been provided a mechanism that will trip the limit switches at predetermined screw positions, regardless of whether the screw is extended by rotating the clevis end of the screw manually or extended by the motor through the gear train. Moreover, in this construction the advancing of the switch actuating tube at a slower rate than the screw advances permits location of the limit switches relatively close together.

We claim:

1. In an electrical switch operating mechanism, a plurality of longitudinally spaced electrical switches, a rotatably driven torque tube and a nut rigidly carried thereby having internal threads of relatively high pitch, a jack screw having external threads to mate with the internal threads of said nut to linearly move said jack screw in either direction depending upon the direction of rotation of said torque tube, a switch actuating tube having internal threads of relatively low pitch to mate with corersponding external threads on said torque tube, an outer member longitudinally splined to said switch actuat ing tube and rigidly secured to said jack screw for transmitting linear movement to said switch actuating tube upon rotational movement of said jack screw, said switch actuating tube having a switch tripping member at its one end to alternately trip said spaced switches.

2. In an electrical switch operating mechanism, a plurality of longitudinally spaced electrical switches, a rotatably driven torque tube and a nut rigidly carried thereby having internal threads of relatively high pitch, a jack screw having external threads to mate with the internal threads of said nut to linearly move said jack screw in either direction depending upon the direction of rotation of said torque tube, a switch actuating tube having internal threads of relatively low pitch to mate with corresponding external threads on said torque tube, an outer member longitudinally splined to said switch actuating tube and rigidly secured to said ack screw for transmitting linear movement to said switch actuating tube upon rotational movement of said jack screw, said switch actuating tube having a switch tripping means adapted to alternately trip said spaced switches.

References Cited in the file of this patent UNITED STATES PATENTS Nelson June 17, 1952 

